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Association for Academic Surgery

CHADS2 score predicts atrial fibrillation followingcardiac surgery

Sohail Sareh, MS,a William Toppen, BA,a Laith Mukdad, BA,a

Nancy Satou, RN,a Richard Shemin, MD,a Eric Buch, MD,b

and Peyman Benharash, MDa,*aDivision of Cardiothoracic Surgery, David Geffen School of Medicine, University of California at Los Angeles, Los

Angeles, CaliforniabDivision of Cardiology, David Geffen School of Medicine, University of California at Los Angeles, Los Angeles,

California

a r t i c l e i n f o

Article history:

Received 4 January 2014

Received in revised form

2 February 2014

Accepted 11 February 2014

Available online 15 February 2014

Keywords:

CHADS2 score

Cardiac surgery

Atrial fibrillation

Risk assessment

Postoperative complications

* Corresponding author. UCLA Division of Ca90095. Tel.: þ1 310 206 6717; fax: þ1 310 206

E-mail address: Pbenharash@mednet.ucl0022-4804/$ e see front matter ª 2014 Elsevhttp://dx.doi.org/10.1016/j.jss.2014.02.007

a b s t r a c t

Background: Atrial fibrillation (AF) following cardiac surgery portends higher morbidity and

increased health expenditure. Although many anatomic and patient risk factors have been

identified, a simple clinical scoring system to identify high-risk patients is lacking. The

CHADS2 score is widely used to predict the risk of stroke in patients with AF. We assessed

the utility of this scoring algorithm in predicting the development of de novo postoperative

atrial fibrillation (POAF) in cardiac surgery patients.

Material and methods: A total of 2120 patients from 2008 to 2013 were identified for inclusion

in our analysis. CHADS2 scores were calculated, and patients grouped into low- (0), inter-

mediate- (1) and high-risk (�2) categories. A multivariate regression model was developed

to account for known risk factors of AF.

Results: Of the2120patients, 344 (16.2%)patients developeddenovoPOAFduring theirprimary

hospitalization. Mean CHADS2 scores for POAF patients and no POAF patients were 2.1 � 1.2

and 1.7 � 1.3 (P < 0.0001), respectively. CHADS2 score was a significant predictor of AF on

multivariate regressionanalysis (adjustedodds ratio, 1.26; 95%confidence interval, 1.14e1.40).

As CHADS2 score increased from 0 to 6, the probability of POAF increased from 11.1% to 32.7%

(P<0.0001).Comparedwiththe low-riskgroup, the intermediate-riskandhigh-riskgroupshad

a 1.73- and 2.58-fold increase inoddsof developing POAF, respectively (P< 0.02 and P< 0.0001).

Conclusions: CHADS2 score is a powerful and convenient predictor of developing POAF. We

recommend its utilization in identifying high-risk patients that may benefit from phar-

macologic prophylaxis.

ª 2014 Elsevier Inc. All rights reserved.

1. Introduction

health care spending in the United States annually [1,2]. Risk

With over 350,000 annual hospitalizations attributed to atrial

fibrillation (AF), it is estimated to account for $6e$26 billion of

rdiac Surgery, 10833 Le C5901.a.edu (P. Benharash).ier Inc. All rights reserved

factors for the development of AF include advanced age, dia-

betes, hypertension, valvular heart disease, heart failure,

obesity, smoking, and chronic renal disease among others [3e5].

onte Avenue, 62-249 Center for Health Sciences, Los Angeles, CA

.

Table 1 e Baseline clinical and operative characteristics.

Characteristic Total (n ¼ 2120) No AF (n ¼ 1776) AF (n ¼ 344) P value

CHADS2 characteristics

Heart failure or EF �40, % 43.4 41.8 51.5 0.001

Hypertension, % 66.2 64.4 76.7 <0.0001

Age, y (mean � SD) 62.1 � 14.7 60.7 � 12.8 69.4 � 11.6 <0.0001

Diabetes mellitus, % 26.7 27.0 24.4 0.32

Cerebrovascular disease, % 10.1 9.9 11.6 0.32

Risk factors

Female, % 33.8 33.6 34.9 0.65

Vascular disease, % 54.9 53.5 61.9 0.004

Smoker, % 21.2 21.4 20.3 0.66

Body mass index, kg/m2 (mean � SD) 27.2 � 0.13 27.2 � 0.14 27.4 � 0.33 0.58

Dyslipidemia, % 55.9 54.2 64.5 0.0004

Anemia, % 49.6 46.5 50.2 0.21

Elevated creatinine, % 14.5 14.9 12.5 0.25

Dialysis, % 6.0 6.3 4.7 0.25

Mitral insufficiency, % 13.8 13.6 15.1 0.45

Aortic insufficiency, % 12.4 11.4 17.4 0.002

Peripheral vascular disease, % 8.1 7.9 9.0 0.48

Preoperative meds

Beta-blocker, % 60.2 59.3 64.8 0.06

Statin, % 58.6 57.0 67.2 0.0005

Aspirin, % 51.2 50.3 56.1 0.05

Anticoagulant, % 13.5 13.7 12.5 0.56

Coumadin, % 4.6 4.7 4.1 0.59

Operative characteristics

Valve surgery, % 44.3 41.6 58.7 <0.0001

Procedure time, min (mean � SD) 330 � 154 323 � 154 364 � 145 <0.0001

Cardiopulmonary bypass time, min (mean � SD) 121 � 89 118 � 90 142 � 75 <0.0001

Perioperative RBC transfusions, n (mean � SD) 1.5 � 2.5 1.5 � 2.5 1.8 � 2.5 0.03

EF ¼ ejection fraction.

j o u r n a l o f s u r g i c a l r e s e a r c h 1 9 0 ( 2 0 1 4 ) 4 0 7e4 1 2408

AF is also a common complication after cardiac operations,with

its incidence ranging between 10% and 60% [6e9]. Although the

underlyingmechanismof postoperative atrial fibrillation (POAF)

is not fully understood, inflammation and oxidative stress from

the cardiac procedure are thought to play a significant role [10].

Adverse outcomes associated with POAF include neurologic,

renal, and infectious complications, as well as death [7,11,12].

Prophylactic regimens such as amiodarone are effective in

reducing the incidence of POAF but limited data are available on

the appropriate identification of high-risk patients who would

benefit most from prophylactic therapy [5,12,13].

The CHADS2 method is a commonly used clinical scoring

system that allows identification of AF patients at high risk of

developing a thromboembolism. Thismethodology is thenused

by practitioners to decide anticoagulation regimens for noncar-

diacsurgicalpatientswithAF[14e16].Because theCHADS2score

consists of risk factors also associated with the development of

AF, its utility in predicting the development of POAF has been

considered. Earlier studies have validated its efficacy in pre-

dicting POAF over the course of multiple years [17,18]. However,

thehighest incidence of POAFoccurswithin 3 d of the procedure

[19]. The focus of this study was to assess the utility of the

CHADS2scoringalgorithmin identifyingpatientsatan increased

risk of developing de novo AF following a cardiac operation.

2. Methods

Between January 2008 and March 2013, 3454 patients who

underwent cardiac surgery at the Ronald Reagan Medical

Center at UCLA were identified. Exclusion criteria for our

analysis included documented history of AF; preoperative

antiarrhythmic drug use; and undergoing an operation

for arrhythmia, ventricular assist device insertion, extracor-

poreal membrane oxygenation, or transplant. All patient

datadincluding demographics, cardiovascular risk factors,

preoperative cardiac status, perioperative data, and post-

operative eventsdwere retrieved electronically from the

institutional database and supplemented with the hospital’s

electronic health records.

A CHADS2 score (0e6) was assigned to each patient based

on medical history, with scoring criteria set on definitions

specified by the STS Adult Cardiac Database Specifications

Version 2.73 [20]. Congestive heart failure (NYHA class II or

greater or left ventricular ejection fraction <40%), hyperten-

sion, age�75 y, and diabetesmellitus were assigned one point

each, whereas stroke and transient ischemic attack received

two points. Patients were then risk-stratified into low-risk (0),

intermediate-risk (1), and high-risk (�2) categories based on

their CHADS2 score according to guidelines published in

CHEST by Lip et al. [21].

The primary end point in this study was the development

of de novo POAF for over 30 s. Hospital discharge and in-

hospital mortality were considered secondary outcomes.

Patient demographics and risk factors are presented as

means with standard deviations, and differences between

POAF and no postoperative atrial fibrillation groups have

been demonstrated via Student t-test. A multivariate logistic

regression model was developed to account for the following

Table 2 e Patient outcomes.

Outcome Total (n ¼ 2120) No AF (n ¼ 1776) AF (n ¼ 344) P value

CHADS2 score (mean � SD) 1.8 � 1.3 1.7 � 1.3 2.1 � 1.2 <0.0001

Low risk (0), % 17.1% 18.8% 8.4% <0.0001

Intermediate risk (1), % 27.4% 28.2% 23.6% 0.08

High risk (�2), % 55.5% 53.1% 68.0% <0.0001

Total intensive care unit, h (mean � SD) 97.7 � 184.2 88.2 � 147.2 147.1 � 307.3 <0.0001

Length of stay, d (mean � SD) 9.4 � 10.8 8.8 � 10.4 12.7 � 12.2 <0.0001

In-hospital mortality, % 2.6% 2.5% 2.9% 0.64

j o u r n a l o f s u r g i c a l r e s e a r c h 1 9 0 ( 2 0 1 4 ) 4 0 7e4 1 2 409

known risk factors and potential confounders: female gender,

obesity, dyslipidemia, history of smoking, anemia (hematocrit

< 36% in females and <39% in males), elevated creatinine

(>1.4 mg/dL in females and >1.5 mg/dL in males), aortic

insufficiency, mitral insufficiency, preoperative beta-blocker

use, preoperative angiotensin-converting enzyme inhibitor

use, preoperative statin use, preoperative aspirin use, preop-

erative warfarin use, preoperative anticoagulation use, valve-

related procedure, procedure time, and perioperative blood

transfusion. To avoid duplication and interdependence, vari-

ables containedwithin the CHADS2 score were not included in

the model. Adjusted odds ratio with 95% confidence intervals,

as well as a predicted probability of developing AF was

calculated for each CHADS2 score. To determine specificity

and sensitivity, an optimal cutoff was set based on the pre-

dicted probability of POAF in the high-risk category. All sta-

tistical analyses were performed using STATA 12.1 software

(StataCorp 2011, College Station, TX), and all tests were

considered significant if P values were <0.005.

Table 3 e Adjusted odds ratio for developing atrialfibrillation.

Variable Odds ratio (95% CI) P value

CHADS2 score 1.26 (1.14e1.40) <0.0001

Low risk (0) 1.00 (Reference)

Intermediate risk (1) 1.73 (1.09e2.73) 0.02

High risk (�2) 2.58 (1.67e4.00) <0.0001

Body mass index, kg/m2 0.99 (0.97e1.01) 0.49

Dyslipidemia 1.09 (0.81e1.46) 0.58

Smoking 0.92 (0.68e1.23) 0.57

Female 1.07 (0.82e1.38) 0.63

Anemia 0.79 (0.61e1.01) 0.06

Elevated creatinine 0.84 (0.56e1.26) 0.40

Dialysis 0.78 (0.42e1.45) 0.44

Peripheral vascular disease 1.01 (0.66e1.55) 0.04

Mitral insufficiency 0.77 (0.54e1.10) 0.15

Aortic insufficiency 1.10 (0.78e1.55) 0.60

Pre-Op anticoagulant 0.89 (0.62e1.28) 0.53

Pre-Op coumadin 0.90 (0.49e1.63) 0.72

Pre-Op beta blocker 1.11 (0.86e1.45) 0.43

Pre-Op statin 1.34 (1.00e1.81) 0.05

Valve surgery 1.94 (1.47e2.56) <0.001

Procedure time 1.00 (1.00e1.00) 0.007

RBC transfusion 1.00 (0.95e1.06) 0.89

Pre-Op ¼ preoperative.

3. Results

Of the 2120 patients (66.2% male) included in the study, 344

(16.2%) patients developed POAF during their primary hospital-

ization period. Baseline characteristics such as demographics,

risk factors, and preoperativemedications are shown in Table 1.

Themean CHADS2 score for the PAOF and NPAOF patients were

2.1� 1.2 and 1.7� 1.3, respectively (P< 0.0001). Figure 1 displays

the distribution of CHADS2 scores between the POAF andNPOAF

patients. Significant differences in secondary outcomes such as

total intensive care unit hours and hospitalization period were

also found (Table 2). When adjusted for risk factors as displayed

in Table 3, a larger preoperative CHADS2 score was associated

with significantly higher odds of developing POAF (adjusted

odds ratio, 1.26; 95%confidence interval, 1.14e1.40; P< 0.0001). A

patient’s probability of developing POAF increased from11.1% to

32.7% as CHADS2 score increased from 0 to 6 (P < 0.0001), as

illustrated in Figure 2. Anemia, preoperative statin use, valve-

related procedures, and procedure time were also significantly

associated with POAF.

In the stratified model, 8.0%, 13.9%, and 19.9% of patients

developed POAF in the low-, intermediate-, and high-risk

groups, respectively. Compared with the low-risk group, pa-

tients in the intermediate-risk and high-risk groups had a 1.73-

and 2.58-fold increase in adjusted odds of developing POAF,

respectively (P< 0.02 and P< 0.0001). This CHADS2 stratification

scheme correctly classified 67.5% of patients, with a specificity

of 70.7% and sensitivity of 50.9% for the development of POAF.

4. Discussion

Postoperative AF is a complex issue that has garnered

particular attention asmore convincing evidence regarding its

negative impact on morbidity and survival is found. Although

this arrhythmia is short-lived and most cases resolve within

6e8 wk, POAF leads to a definite increment in long-term

mortality and cost of health care. Increased adrenergic drive,

atrial stretch, and inflammation in the period following sur-

gery have been cited as possible causes of POAF [10]. Perhaps,

a relevant question to ask is whether AF is simply a marker of

worse cardiovascular risks.

The goal of this studywas to assess the clinical utility of the

CHADS2 score in identifying patients at a higher risk of

developing de novo POAF. Our analysis has indicated that

patients with an elevated CHADS2 score (�2) have a signifi-

cantly higher risk of developing POAF comparedwith a patient

with a low CHADS2 score (0). Because the CHADS2 score is an

aggregate of risk factors associated with the long-term

development of AF, our findings are not surprising. A recent

nationwide cohort study from Taiwan found the CHADS2score to be useful in risk stratification over the course of a

Fig. 1 e Distribution of CHADS2 Score.

j o u r n a l o f s u r g i c a l r e s e a r c h 1 9 0 ( 2 0 1 4 ) 4 0 7e4 1 2410

9.0-y mean follow-up period [18]. However, our analysis has

indicated that the CHADS2 score also serves as a reliable

predictor of developing AF in the immediate postoperative

period. The majority of patients in our analysis were correctly

classified between POAF and no postoperative atrial fibrilla-

tion groups using our risk stratification scheme, further con-

firming its utility as a predictor of de novo AF.

Moreover, our logistic regressionmodel found that patients

undergoing a valve-related procedurewere at a significant risk

of developing AF. Prior studies have attributed this increased

risk to longer bypass and cross-clamp times associated with

valve procedures, as well as surgical cannulation and dissec-

tion techniques [7,22]. In addition, preoperative statin use was

also associated with the development of AF. Current literature

is inconsistent regarding the protective effects of statin use on

the development of POAF [23,24]. However, a recent study

suggests that statins may be beneficial only in patients with a

high CHADS2 score [25]. In our analysis, we accounted for a

substantial number of factors such as the aforementioned in

an attempt to validate our findings of the predictive value of

the CHADS2 score.

Although recommended guidelines for antiarrhythmic

prophylaxis have been established by multiple organizations

Fig. 2 e Probability of POAF with 95% confidence intervals.

[26,27], few institutions have standardized their prophylactic

approach and the practice is widely underused [28]. This is in

part due to the side effects and costs of antiarrhythmic agents.

Amiodarone, for instance, is associated with heart block, as

well as pulmonary, hepatic, and thyroid toxicity. In this

retrospective study of cardiac surgical patients, the CHADS2score functioned as a practical and effective risk stratification

tool for the development of POAF. Therefore, institutions may

use this scoring system to formulate a targeted prophylaxis

strategy. Additional investigation is warranted via a prospec-

tive study that includes the CHADS2 risk schema in deter-

mining prophylactic management of patients.

This study has several limitations. The retrospective and

single-center nature of this study limits generalization of our

findings. However, the large number of patients, the rigorous

reporting of POAF at our institution, and the vast set of vari-

ables in the database serve to offset this shortcoming. The low

incidence of AF in this cohort may be explained by the fact

that we excluded patients with preoperative AF. Patients with

AF before surgery are thought to have substrate changes in the

structure of the atria that predisposes them to further epi-

sodes [19]. Moreover, although large left atrial volume has

been independently associated with the development of

POAF, consistent data on this preoperative factor were not

available for our patient population [29]. Thus, wewere unable

to adjust for this factor in our multivariate analysis.

5. Conclusion

In this retrospective study of adult cardiac surgical patients,

we evaluated the utility of the CHADS2 scoring system in

predicting de novo POAF. Patients with a CHADS2 score of �2

have a higher probability of developing AF compared with

those with a score of <2. This scoring system could be used to

develop a targeted prophylaxis strategy to reduce AF after

cardiac surgery.

Acknowledgment

The authors thank Peter Hsiue and the UCLA Statistical

Consulting Group for their invaluable contributions to this

project.

Author Contributions: S.S.: Study design, data collection,

data analysis, data interpretation, article drafting; W.T.: Data

analysis, data interpretation, article drafting, critical re-

visions; L.M.: Data collection, article drafting, critical re-

visions; N.S.: Data collection, data analysis, critical revisions;

R.S.: Study concept, study design, data interpretation, critical

revisions; E.B.: Study design, data interpretation, critical

revisions; P.B.: Study concept, study design, data collection,

data analysis, data interpretation, article drafting, critical

revisions.

Disclosure

The authors reported no proprietary or commercial interest in

any product mentioned or concept discussed in this article.

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